The present invention relates to network interfacing, and more particularly, to methods and systems for controlling transmission of data between network stations connected to a telephone line medium.
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media.
Conventional local area network architectures use media access controllers operating according to half-duplex or full duplex Ethernet (ANSI/IEEE standard 802.3) protocol using a prescribed network medium, such as 10 BASE-T. Newer operating systems require that a network station to be able to detect the presence of the network. In an Ethernet 10 BASE-T environment, the network is detected by the transmission of a link pulse by the physical layer (PHY) transceiver. The periodic link pulse on the 10 BASE-T media is detected by a PHY receiver, which determines the presence of another network station transmitting on the network medium based on detection of the periodic link pulses. Hence, a PHY transceiver at Station A is able to detect the presence of Station B, without the transmission or reception of data packets, by the reception of link pulses on the 10 BASE-T medium from the PHY transmitter at Station B.
Efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines instead of established local area network media such as 10 BASE-T. Such an arrangement, referred to herein as a home network environment, provides the advantage that existing telephone wiring in a home may be used to implement a home network environment. However, telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home, for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone lines suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard POTS telephones, and electrical systems such as heating and air conditioning systems, etc.
An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely on the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak-to-peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmit clock or transmit data from the received pulse becomes substantially difficult.
The variation in a received network signal creates problems in determining an optimum threshold comparator value in comparators used to recover the network clock and data signals from the received network signals. One proposal is to adapt the current threshold levels during an access ID (AID) time, where a binary search is used to determine the successive significant bit value for the comparator circuit threshold based on successive received pulses. Hence, the eight pulses received during the AID interval are used to set an eight-bit threshold level for a comparator. However, the wide range of peak voltages in the incoming network signal may cause saturation of the receiver circuitry if the received network signal is substantially large, for example on the order of two volts peak voltage. Conversely, a network signal having a peak voltage on the order of 10 to 20 millivolts requires a receiver having a substantially wide dynamic range, else the smaller network signals cannot be distinguished from noise signals.
There is a need for a network station having a physical layer transceiver capable of reliably recovering data from a received network signal on a telephone line medium.
There is also a need for a physical layer transceiver capable of adapting to a wide dynamic range of received network signals in a cost-efficient manner.
There is also a need for an arrangement in a physical transceiver that enables an input amplifier gain and comparator threshold values to be set within an access identifier interval without loss of resolution in the comparator threshold values.
These and other needs are obtained by the present invention, where a digital controller is configured for determining a gain setting for the input amplifier during a first portion of the access identifier interval, and determining the data threshold value and a peak threshold value for first and second comparator circuits within a second portion of the access identifier interval. The data threshold value and peak threshold values are determined within the second portion of the access identifier interval by a comparison of the received network signals to threshold values supplied to first and second comparator circuits normally used for peak detection and data (e.g., mid-point) detection, respectively.
According to one aspect of the present invention, a network station configured for receiving network signals from another network station via a telephone line medium includes an input amplifier for selectively amplifying a received network signal according to a selected one of a plurality of gain settings and outputting an amplified network signal, an envelope detector configured for outputting an envelope signal in response to the amplified network signal, first and second comparator circuits configured for outputting first and second comparison signals indicating whether the envelope signal exceeds first and second threshold values, respectively, and a digital controller. The digital controller is configured for setting the selected one gain setting and the first and second threshold values within a prescribed access identifier interval specified by a prescribed number of the received network signals from the telephone line medium. The digital controller determines the selected one gain setting during a first portion of the prescribed access identifier interval, and a peak threshold value and data threshold value for the respective first and second threshold values during a second portion of the prescribed access identifier interval, the peak threshold value substantially corresponding to a detected peak of the envelope signal. Use of an input amplifier for selectively amplifying a received network signal enables the physical layer transceiver to optimize reception of a data packet, eliminating the occurrence of input amplifier saturation and selectively amplifying network signals for improved sensitivity, balancing the need for a good signal to noise ratio using a high-sensitivity receiver. Moreover, the use of first and second comparator circuits enables the digital controller to identify a peak threshold value substantially corresponding to a detected peak of the envelope signal within a second portion of the prescribed access identifier interval. Hence, use of the first and second comparator circuits enables use of advanced searching techniques more efficient than binary search techniques, enabling determination of a peak threshold value in a minimal amount of time.
Another aspect of the present invention provides a method of configuring a network station transceiver for reception, from a telephone line medium, of network data signals contiguously following a prescribed number of network access identifier signal pulses defining an access identifier interval. The method includes determining a gain setting for an input amplifier, configured for outputting an amplified network signal to an envelope detector, within a first portion of the access identifier interval, and determining a data threshold value and a peak threshold value for first and second comparator circuits, configured for identifying whether an envelope signal generated based on the amplified network signal exceeds supplied threshold values, within a second portion of the access identifier interval.
Additional advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.